Summary

It's a 3D printed Z nut with screw M6.
Printed with nylon fishing line.
Nylon nut is very strength, smooth, no backlash and no wobble.
Recomended layer height 0.15 mm for better print screw M6 with 1 mm steps.
http://www.youtube.com/watch?v=tmoXreZrD-o&list=UUnyyenl1R2XbUurYMoan9Ww
http://www.youtube.com/watch?v=NMUDsh3YjwU
http://www.youtube.com/watch?v=CHxPvpeDKpI